ALPO COMET NEWS FOR Mar 2017
This month visual observers will be able to follow four bright comets (five, if you include 2P/Encke though it may already be too close to the Sun for most observers as the month begins). Comet 45P/Honda-Mrkos-Pajdusakova is rapidly fading after passing 0.08 au from Earth last month. 41P/Tuttle-Giacobini-Kresak takes its turn passing close to the Earth (0.14 au) on April 1 and may reach 6th magnitude by the end of March. Two long-period comets should also become brighter than 10th magnitude [C/2015 ER61 (PANSTARRS) and C/2015 V2 (Johnson)].
Last month the Comet Section received comet magnitude estimates for comets 2P/Encke, 41P/Tuttle-Giacobini-Kresak and 45P/Honda-Mrkos-Pajdusakova from Salvador Aguirre and Carl Hergenrother. CCD images were also received for comets 2P/Encke, 41P/Tuttle-Giacobini-Kresak, 45P/Honda-Mrkos-Pajdusakova and C/2015 V2 (Johnson) from Richard Owens, Efrain Morales Rivera and John D. Sabia.
2P/Encke [Perihelion on 2017 March 10 at 0.34 au]
If you live in the northern hemisphere and haven’t see Encke yet this apparition, the clock is ticking. On March 1, Encke will be a 7th-8th magnitude object located low in the western evening sky at an elongation of only 24 degrees. The comet rapidly drops closer to the Sun and will be invisible only a few days into March. A second opportunity to see Encke will occur between March 9 and 14 via our computers as the comet will be within the field-of-view of the LASCO C3 instrument on the SOHO spacecraft. Observers south of the equator will be able to observe Encke towards the end of the month as it reappears in the morning sky at 8th magnitude. The comet starts the month at a heliocentric distance of 0.41 au. Perihelion occurs on March 10 at 0.34 au. By the end of the month it will be at 0.64 au from the Sun. Its distance from Earth drops from 0.81 au on the 1st to 0.66 au on the 12th before increasing to 0.91 au at the end of the month. Encke will be traveling through Pisces (Mar 1-10) and Aquarius (11-31).
45P/Honda-Mrkos-Pajdusakova [Perihelion on 2016 December 31 at 0.53 au]
Comet 45P/Honda-Mrkos-Pajdusakova is rapidly fading after its close approach to Earth (0.08 au) on Feb 11. Though it was a small condensed object with a long gas tail prior to perihelion, it became a large, low surface brightness object post-perihelion. As is often the case with such objects, observing conditions and the equipment used can greatly affect the view. The comet can easily be missed if the sky was too bright or too high of a magnification was used. As a result, the comet was considered a disappointment by some. Salvador Aguirre and Carl Hergenrother were able to observe the comet in 7×50 and 10×50 binoculars at around magnitude 6.5 a few days prior to close approach. In my 10×50s the coma was over a half degree in diameter. Unfortunately the date of close approach and the days after were compromised by a nearly Full Moon. By the time the Moon was out of the sky, 45P had faded to magnitude 7.6. This month the comet starts at 9th magnitude but continues fading to 13th by the end of March as it moves through Leo (Mar 1-2, 6-9, 13-31) and Leo Minor (2-6, 8-13). Its distances from the Sun and Earth increase from 1.23 to 1.64 au and from 0.25 to 0.74 au, respectively.
41P/Tuttle-Giacobini-Kresak [Perihelion on 2017 Apr 12 at 1.05 au]
Comet 41P/Tuttle-Giacobini-Kresak will also make an impressive close approach to Earth. Though it won’t come as close as 45P did back in February, 41P is an intrinsically brighter comet and will appear brighter in apparent magnitude. Still, 41P may be more difficult to see than its brightness suggests to those observing under less than dark skies. The comet starts the month around magnitude 9.6 and will brighten to magnitude 8.3 on 3/11, 7.2 on 3/21, and 6.5 on 3/31. Closest approach occurs on April 1 at 0.14 au. This is nearly the closest this comet can come to Earth on its current orbit and it won’t pass this close again till 2066.
T-G-K is outburst prone and experienced two 10-magnitude outbursts in 1973. Smaller outbursts also occurred in 1995 and 2001. If T-G-K were to experience an outburst during this return it could become a naked eye object. During March, T-G-K moves from 1.19 to 1.06 au from the Sun and 0.22 to 0.14 au from Earth. It will be located in Leo (Mar 1-5), Leo Minor (5-12), Ursa Major (12-29), Draco (29-31) as its elongation drops from 155 to 110 degrees in the evening sky.
C/2015 V2 (Johnson) [Perihelion on 2017 June 12 at 1.64 au]
Comet Johnson is inbound with a perihelion of 1.64 au and close approach to Earth at 0.81 au this summer. It is well placed for northern observers through perihelion. Its rate of brightening has been slow so this month it is only expected to brighten from magnitude 10.4 to 9.6. During March, it is a morning object in Hercules (Mar 1-31) at an elongation that increases from 101 to 108 degrees. It starts the month 2.13 au from the Sun and 1.70 au from Earth. At the end of the month, these values decrease to 1.90 au from the Sun and 1.34 au from Earth.
C/2015 ER61 (PANSTARRS) [Perihelion on 2017 May 9 at 1.04 au]
C/2015 ER61 (PANSTARRS) will reach perihelion on May 9 at 1.04 au from the Sun but never gets closer to Earth than 1.18 au. As a result, ER61 may only brighten to 8th magnitude at is brightest in May. For northern observers, it will be located low in the morning sky. It will be better placed for southern observers. This month its distance from the Sun increases from 1.54 au to 1.23 au. Its geocentric distance grows from 1.58 to 1.23 au as it travels through Sagittarius (Mar 1-27) and Capricornus (27-31). It is currently 10-11th magnitude and may brighten to 9th magnitude by the end of the month though its rate of brightening also appears to be rather slow.
73P/Schwassmann-Wachmann 3 [Perihelion on 2017 March 16 at 0.97 au]
A newly discovered component of the split comet 73P/Schwassmann-Wachmann 3 was observed in outburst during February. Component 73P-BT is currently 11-12th magnitude and located within arc minutes of the primary component 73P-C (a little fainter at 13th magnitude). CCD imagers and large aperture visual observers are asked to monitor this comet for additional outbursts or splitting events. The comet is located low in the eastern morning sky and will only get lower as the month progresses. 73P has a long history of splitting events following an initial split in 1995. Though hundreds to thousands of components were observed during its close flyby of Earth in 2006, components C and BT are the only two known to be currently active.
As always, the Comet Section is happy to receive all comet observations, whether images, drawings or magnitude estimates.
- Carl Hergenrother (ALPO Comet Section Coordinator)